Sterically Hindered Amines and Associated Methods

ABSTRACT

Amine compositions comprising sterically hindered amines and associated methods are provided. In some embodiments, amine compositions of the present disclosure may be useful for selective removal of H 2 S from an acidic gas stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/418,425 filed Dec. 1, 2010, the entiredisclosure of which is incorporated by reference.

BACKGROUND

The present disclosure generally relates to sterically hindered amines,and more specifically, to the production of sterically hindered aminesfrom polyethylene glycol and tertiarybutylamine and their use in acidicgas removal.

Various amine solutions have been used for the removal of acidic gasesfrom gases and liquids. Common acidic gases may include, CO₂, H₂S, CS₂,HCN, COS and oxygen and sulfur derivatives of C₁ to C₄ hydrocarbons. Ingeneral, the treatment of gases and liquids containing acidic gases,such as CO₂ and H₂S, with certain amine solutions typically results inthe simultaneous removal of substantial amounts of both CO₂ and H₂S.However, in some instances, it may be desirable to treat acidic gasmixtures containing both CO₂ and H₂S so as to selectively remove H₂Sfrom the mixture, thereby minimizing removal of the CO₂. Selectiveremoval of H₂S results in a relatively high H₂S/CO₂ ratio in theseparated acid gas, which may aid in the conversion of H₂S to elementalsulfur using the Claus process.

Sterically hindered amines have been used for the selective removal ofH₂S from gaseous mixtures. One method of producing sterically hinderedamines has included the catalytic tertiarybutylamination of triethyleneglycol to produce bis-(tertiarybutylaminoethoxy) amine andethoxyethanoltertiarybutylamine. However, this process has drawbacksbecause under CO₂ rich conditions and/or highbis-(tertiarybutylaminoethoxy) ethane content, the amine salt canprecipitate out of solution during the acid gas removal process andfouling of the equipment may occur. In addition, the costs associatedwith the starting reaction materials necessary to produce stericallyhindered amines are generally high and prior art processes havegenerally yielded high levels of undesirable by-products, resulting inonly 25-30% useable product.

SUMMARY

The present disclosure generally relates to sterically hindered amines,and more specifically, to the production of sterically hindered aminesfrom polyethylene glycol and tertiarybutylamine and their use in acidicgas removal.

In one embodiment, the present disclosure provides an amine compositioncomprising a mixture of at least two sterically hindered aminescomprising a first amine with the formula:

and a second amine with the formula:

wherein x is an integer from 3 to 14; y is an integer from 3 to 14, andthe weight ratio of the first amine to the second amine is about 2.5:1to about 6:1.

In another embodiment, the present disclosure provides a method ofmaking an amine composition comprising reacting a polyethylene glycolwith a tertiarybutylamine in the presence of a nickel-basedhydrogenation catalyst to form an amine composition comprising a mixtureof at least two sterically hindered amines, wherein the aminecomposition comprises at least a first amine with the formula:

and a second amine with the formula:

wherein x is an integer from 3 to 14; y is an integer from 3 to 14, andthe weight ratio of the first amine to the second amine is about 2.5:1to about 6:1.

In yet another embodiment, the present disclosure provides a methodcomprising contacting a gaseous stream comprising sulfur-containingcompounds with an amine composition comprising a mixture of at least twosterically hindered amines, wherein the amine composition comprises atleast a first amine with the formula:

and a second amine with the formula:

wherein x is an integer from 3 to 14; y is an integer from 3 to 14, andthe weight ratio of the first amine to the second amine is about 2.5:1to about 6:1.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

DRAWINGS

Some specific example embodiments of the disclosure may be understood byreferring, in part, to the following description and the accompanyingdrawings.

FIG. 1 is a graph showing the effect of CO₂ concentration on H₂Sremoval.

FIG. 2 is a graph showing the effect of CO₂ concentration effect on CO₂absorption.

FIG. 3 is a graph showing the change of H₂S in a treated gas as afunction of the amine circulation rate.

While the present disclosure is susceptible to various modifications andalternative forms, specific example embodiments have been shown in thefigures and are herein described in more detail. It should beunderstood, however, that the description of specific exampleembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, this disclosure is to cover allmodifications and equivalents as illustrated, in part, by the appendedclaims.

DESCRIPTION

The present disclosure generally relates to sterically hindered amines,and more specifically, to the production of sterically hindered aminesfrom polyethylene glycol and tertiarybutylamine and their use in acidicgas removal.

The present disclosure is based, at least in part, on the observationthat under certain conditions, such as CO₂ rich conditions and/or highbis-(tertiarybutylaminoethoxy) ethane content, certain amines forselectively removing H₂S gas may become phase separated. In someembodiments, the present disclosure addresses this problem by, amongother things, reacting a higher molecular weight polyethylene glycolwith a tertiarybutylamine to produce a mixture of sterically hinderedamines that provides good performance without the problem of phaseseparation. In addition, in some embodiments, the sterically hinderedamines of the present disclosure may be made without the need for asolvent, thereby simplifying their production. Furthermore, in someembodiments, the methods of the present disclosure may be consideredmore “environmentally friendly” in that they produce higher yields ofdesirable amine products with minimal to no production of undesirableby-products, which may also reduce the costs associated with makingsterically hindered amines.

In one embodiment, the present disclosure provides an amine compositioncomprising a mixture of at least two sterically hindered amines with thefollowing formulas:

wherein x is an integer ranging from 3 to 14, y is an integer rangingfrom 3 to 14, and the weight ratio of a first sterically hindered amine(1) to a second sterically hindered amine (2) is about 2.5:1 to about6:1. In some embodiments, the weight ratio of a first stericallyhindered amine (1) to a second sterically hindered amine (2) is about4:1.

In other embodiments, an amine composition of the present disclosure maycomprise a mixture of at least two sterically hindered amines, a firststerically hindered amine having the chemical formula shown in (1)wherein x is an integer ranging from 7 to 14; and a second stericallyhindered amine having the chemical formula shown in (2) wherein y is aninteger ranging from 7 to 14.

In addition to the above mentioned amine compositions, the presentdisclosure also provides methods of making these amine compositionscomprising reacting a polyethylene glycol with a tertiarybutylamine inthe presence of a nickel-based hydrogenation catalyst. The polyethyleneglycol suitable for use in the present disclosure generally has amolecular weight between about 180 to about 1000 grams per mole (g/mol).In some specific embodiments, the polyethylene glycol may have amolecular weight between about 180 to about 400 g/mol. In some specificembodiments, the polyethylene glycol may have a molecular weight betweenabout 200 to about 300 g/mol.

Nickel-based hydrogenation catalysts suitable for use in the presentdisclosure may include any nickel based catalyst capable of catalyzing areaction between polyethylene glycol and a tertiarybutyl amine. In oneembodiment, a suitable hydrogenation catalyst comprises thosenickel-based catalysts disclosed in U.S. Pat. Nos. 7,683,007 and7,196,033, both of which are hereby incorporated by reference in theirentirety. As will be recognized by one of skill in the art, thehydrogenation catalyst may be in any suitable form, including but notlimited to, pellets, tablets, extrudates, spheres, etc. Additionally, asuitable catalyst can either be unsupported or deposited on a supportmaterial, as is known to those skilled in the art, such as alumina,silica, etc.

In some embodiments, reduction of the hydrogenation catalyst may becarried out in situ while conducting the process by the presence ofhydrogen. Hydrogen, however, is not essential to conducting the processbut may be employed, for example, to minimize catalyst deactivation.

In some embodiments, the sterically hindered amines of the presentdisclosure may be made without the need for a solvent, therebysimplifying their production. However, in some embodiments, an inertsolvent may be included in the reaction medium if desired. Examples ofsuitable solvents may include, but are not limited to, a cyclic orlinear ether or a hydrocarbon containing compound in which the reactantswill dissolve.

The amination process may be carried out in any suitable reactor,including, but not limited to, a fixed-bed reactor, a fluid-bed reactor,a continuous stirred reactor, or a batch reactor. In one embodiment, thereaction of polyethylene glycol with a tertiarybutylamine may be carriedout in a reactor under a pressure of about 500 to about 3000 prig and atemperature of from about 160° C. to about 240° C.

In some embodiments, the sterically hindered amines of the presentdisclosure may be placed in a liquid medium prior to use, such as water,an organic solvent and mixtures thereof. In addition, the stericallyhindered amines may also be used in conjunction with a wide range ofadditives typically employed in selective gas removal processes, such asanti-foaming agents, antioxidants, corrosion inhibitors, etc. in aneffective amount. In some embodiments, the sterically hindered amines ofthe present disclosure may also be used in conjunction with a strongacid, such as sulfuric acid, sulfurous acid, phosphoric acid,phosphorous acid, pyrophosphoric acid, acetic acid, formic acid, adipicacid, benzoic acid, etc.

As mentioned above, the sterically hindered amines of the presentdisclosure may be useful in selectively removing H₂S from an acidic gasmixture. Acidic gas mixtures suitable for use in the present disclosureinclude any gas mixture that comprises an acidic gas for which acid gasremoval is desired. Examples of suitable acidic gas mixtures are thosecomprising H₂S, and optionally other gases such as CO₂, N₂, CH₄, H₂, CO,COS, HCN, C₂H₄, NH₃, etc. Acidic gas mixtures may include various typesof gases, including, but not limited to, combustion gases, refinerygases, town gas, natural gas, syn gas, water gas, propane, propylene,heavy hydrocarbon gases, etc.

In one embodiment, the present disclosure also provides a method forremoving sulfur-containing compounds from a gaseous stream comprisingcontacting the gaseous stream with an amine composition of the presentdisclosure. In general, the gaseous stream and an amine composition ofthe present disclosure may be brought into contact using anyconventional means, such as a tower or packed vessel. For example, inone embodiment, a gaseous stream may be fed into a lower portion of anabsorption tower while an amine composition of the present disclosure isfed into an upper portion of the tower. The gaseous stream and the aminecomposition may come into contact with each other such thatsulfur-containing compounds, such as H₂S, may be selectively absorbed bythe amine composition. The amine composition containing the selectivelyabsorbed sulfur-containing compounds may then emerge near the bottom orlower portion of the tower, which the remaining normally gaseous stream,emerges from the upper portion of the tower.

In some embodiments, after contacting the gaseous stream with an aminecomposition of the present disclosure, the amine composition containingthe sulfur-containing compounds may be at least partially regenerated sothat it may be reused.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the invention.

EXAMPLES Example 1 Preparation of PEG-240

About 16 pounds of diethylene glycol and 130 grams ofdimethylcyclohexylamine were charged to an 8-gallon reactor. The reactorwas then purged with nitrogen and heated to about 85° C. Then, about 20pounds of ethylene oxide were added to the reactor, as the temperatureof the reactor was maintained at around 90° C. Upon the conclusion ofthe reaction, the reaction mixture was purged with nitrogen at about 80°C. for about 20 minute and then screen filtered. The resulting productwas analyzed to have a hydroxyl value of 469.7 mg KOH/g.

Example 2 Preparation of Amine

PEG-240 from Example 1 and tertiarybutylamine were each continuously fedto a tubular reactor that was charged with 250 cc of a nickel catalystat feed rates of 120 g/hr and 300 g/hr, respectively. The reactorpressure and temperature (hot oil temperature) were maintained at 2000psig and 200° C. The reactor effluent was stripped of excesstertiarybutylamine and other light materials. The resulting product wasanalyzed to contain 4.28 meq/g of total amine.

Example 3 Preparation of Amine from TEG

Triethylene Glycol and tertiarybutylamine were each continuously fed toa tubular reactor that was charged with 250 cc of a nickel catalyst atfeed rates of 115 g/hr and 300 g/hr, respectively. The reactor pressureand temperature (hot oil temperature) were maintained at 2000 prig and200° C. The reactor effluent was stripped of excess tertiarybutylamineand other light materials. The resulting product was analyzed to contain5.72 meq/g of total amine.

Example 4 Effect of CO₂ Concentration on H₂S Removal and CO₂ Absorption

13500 grams of a 45 wt % sterically hindered amine solution wereprepared and charged to a gas treating unit containing an absorber and astripper connected together in a continuous flow. The lean aminetemperature was controlled at approximately 70° C., while the stripperwas heated to approximately 117° C. The H₂S, CO₂ and N₂ flowrate intothe absorber was varied to obtain the desired CO₂ concentration (0 to65%) and H₂S concentration (6000 ppm). The amine circulation flow wascontrolled at 115 ml/min. After approximately 4 hours, the gas treatingunit had equilibrated and samples of the gas coming off the absorber andstripper were collected and analyzed by on line gas chromatograph. Thevolume of gas coming in and out of the absorber was also measured. Thesame procedures were repeated for 45% MDEA. The results are shown inFIG. 1 and FIG. 2. The data show the sterically hindered amine has muchbetter scrubbing of H₂S compared to MDEA and have similar performance interms of CO₂ absorption. Accordingly, an amine composition of thepresent disclosure demonstrates a higher selectivity for H₂S compared toMDEA.

Example 5 Effect of Amine Circulation Flow on H₂S Removal

13500 grams of a 45 wt % sterically hindered amine solution wereprepared and charged to a gas treating unit containing an absorber and astripper connected together in a continuous flow. The lean aminetemperature was controlled at approximately 70° C. while the stripperwas heated to approximately 117° C. The H₂S, CO₂ and N₂ flowrate intothe absorber were controlled at the desired rate to obtain theapproximate 43% CO₂ and 6000 ppm H₂S in the feed. The amine circulationflow was varied from 110 ml/min to 180 ml/min. After approximately 4hours, the gas treating unit had equilibrated and samples of the gascoming off the absorber and stripper were collected and analyzed by online gas chromatograph. The volume of gas coming in and out of theabsorber was also measured. The same procedures were repeated for 45%MDEA. The results are shown in FIG. 3. The data show the stericallyhindered amine has much better scrubbing of H₂S compared to MDEA.

Example 6 Effect of Adding Phosphoric Acid on H₂S Removal

13500 grams of a 45 wt % sterically hindered amine solution wereprepared and charged to a gas treating unit containing an absorber and astripper connected together in a continuous flow. The lean aminetemperature was controlled at approximately 70° C. while the stripperwas heated to approximately 117° C. H₂S, CO₂ and N₂ flowrate into theabsorber were controlled at the desired rate to obtain the approximate43% CO₂ and 6000 ppm H₂S in the feed. The amine circulation flow wascontrolled at 200 ml/min. After approximately 4 hours, the gas treatingunit had equilibrated and samples of the gas coming off the absorber andstripper were collected and analyzed by on line gas chromatograph. 34grams of a 85% phosphoric acid solution was then injected into thestripper reboiler with N₂. The samples from the absorber and stripperwere collected periodically until the treated gas reading was steady andthe data were recorded. The lean and rich samples were also collectedand H₂S content was determined by titration with silver nitrate. Thesame procedures (with and without phosphoric acid added) were repeatedfor 45% MDEA. The results are shown in Table 1 below. The datademonstrate a sterically hindered amine with a small amount ofphosphoric acid addition significantly reduces the H₂S in the treatedgas. The acid addition didn't improve the H₂S treating capability of 45%MDEA due to the already lower lean loading in the MDEA (3 grain/gallonbefore acid addition) and further reducing the lean loading didn'timprove the performance.

TABLE 1 Treated H₂S (ppm) from absorber (200 ml/min amine circulationrate) No acid added 34 grams of Phosphoric in the solution acid in thesolution 45% MDEA solution 501 500 45% Sterically 292 205 hindered aminesolution

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. While compositions and methods aredescribed in terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps. Allnumbers and ranges disclosed above may vary by some amount. Whenever anumerical range with a lower limit and an upper limit is disclosed, anynumber and any included range falling within the range is specificallydisclosed. In particular, every range of values (of the form, “fromabout a to about b,” or, equivalently, “from approximately a to b,” or,equivalently, “from approximately a-b”) disclosed herein is to beunderstood to set forth every number and range encompassed within thebroader range of values. Also, the terms in the claims have their plain,ordinary meaning unless otherwise explicitly and clearly defined by thepatentee. Moreover, the indefinite articles “a” or “an”, as used in theclaims, are defined herein to mean one or more than one of the elementthat it introduces. If there is any conflict in the usages of a word orterm in this specification and one or more patent or other documentsthat may be incorporated herein by reference, the definitions that areconsistent with this specification should be adopted.

1. An amine composition comprising: a mixture of at least two stericallyhindered amines comprising a first amine with the formula:

and a second amine with the formula:

wherein x is an integer from 3 to 14; y is an integer from 3 to 14, andthe weight ratio of the first amine to the second amine is about 2.5:1to about 6:1.
 2. The amine composition of claim 1 wherein x is aninteger from 7 to
 14. 3. The amine composition of claim 1 wherein y isan integer from 7 to
 14. 4. The amine composition of claim 1 wherein xis an integer from 7 to 14 and y is an integer from 7 to
 14. 5. Theamine composition of claim 1 wherein the weight ratio of the first amineto the second amine is about 4:1.
 6. A method of making an aminecomposition comprising: reacting a polyethylene glycol with atertiarybutylamine in the presence of a nickel-based hydrogenationcatalyst to form an amine composition comprising a mixture of at leasttwo sterically hindered amines, wherein the amine composition comprisesat least a first amine with the formula:

and a second amine with the formula:

wherein x is an integer from 3 to 14; y is an integer from 3 to 14, andthe weight ratio of the first amine to the second amine is about 2.5:1to about 6:1.
 7. The method of claim 6 wherein x is an integer from 7 to14.
 8. The method of claim 6 wherein y is an integer from 7 to
 14. 9.The method of claim 6 wherein x is an integer from 7 to 14 and y is aninteger from 7 to
 14. 10. The method of claim 6 wherein the weight ratioof the first amine to the second amine is about 4:1.
 11. The method ofclaim 6 wherein the polyethylene glycol has a molecular weight of fromabout 180 to 1000 g/mol.
 12. The method of claim 6 wherein thepolyethylene glycol has a molecular weight of from about 180 to 400g/mol.
 13. The method of claim 6 further comprising contacting a gaseousstream comprising sulfur-containing compounds with the aminecomposition.
 14. The method of claim 6 wherein the polyethylene glycoland the tertiarybutylamine are reacted in a fixed-bed reactor, afluid-bed reactor, a continuous stirred reactor or a batch reactor. 15.The method of claim 6 wherein the polyethylene glycol and thetertiarybutylamine are reacted at a temperature of from about 160° C. toabout 240° C.
 16. A method comprising: contacting a gaseous streamcomprising sulfur-containing compounds with an amine compositioncomprising a mixture of at least two sterically hindered amines, whereinthe amine composition comprises at least a first amine with the formula:

and a second amine with the formula:

wherein x is an integer from 3 to 14; y is an integer from 3 to 14, andthe weight ratio of the first amine to the second amine is about 2.5:1to about 6:1.
 17. The method of claim 16 further comprising contactingthe gaseous stream with a strong acid.
 18. The method of claim 18wherein the strong acid is phosphoric acid or sulfuric acid.
 19. Themethod of claim 16 wherein x is an integer from 7 to 14 and y is aninteger from 7 to
 14. 20. The method of claim 16 wherein the weightratio of the first amine to the second amine is about 4:1.